NMDA receptors play critical roles in the regulation of synaptic plasticity, neuronal development and several neurological and psychiatric diseases. Studies in the last ten years have shown that NMDA receptors bind to the PSD95/SAP90 family of adaptor protein to form a large macromolecular signaling complex. The PSD95/SAP90 protein family appears to play a critical role in the in the coupling of NMDA receptors to downstream signal transduction pathways and in the synaptic targeting of NMDA and AMPA receptors. In this research proposal we plan to study the structure, function and regulation of the NMDA receptor macromolecular signaling complex and the role of this complex in synaptic transmission and plasticity. Firstly, studies in our laboratory have shown that dynamic phosphorylation of the NMDA receptor by casein kinase II disrupts NMDA receptor binding to the PSD95/SAP90 protein and thus may play a critical role in the regulation of NMDA receptor signaling. We plan to study the regulation of this phosphorylation and examine its effect on NMDA receptor function and downstream signaling. Secondly, we previously showed that SynGAP, a synapse-specific RasGAP directly interacts with SAP102 and PSD95/SAP90 and that this interaction is important for regulation of synaptic transmission. We will further investigate the regulation of SynGAP and its role in Ras signaling at the molecular level using neurons transfected with wildtype and mutant forms of SynGAP and with SynGAP knock-out mice. Finally, we will identify and characterize synaptic substrates for MAP kinase signaling pathway enzymes including the ERK, RSK, JNK and p38 protein kinases. These kinases, which are all present in the NMDA receptor-signaling complex, play critical roles in the regulation of synaptic transmission and plasticity. However, the synaptic substrates for these kinases are largely unknown. The role of phosphorylation of MAP kinase synaptic substrates in modulating synaptic function will be determined. These studies will investigate the function of the NMDA receptor protein signaling complex at three different levels and will help elucidate the function of this complex in excitatory synaptic function and its potential role in neurological and psychiatric diseases.